1. Field of the Invention
The present invention relates to an image processing apparatus having a function of identifying characteristics of an input image.
2. Related Background Art
In recent years, digital color copying machines are becoming popular. In a copying machine of this type, a color original is color-separated and read in units of pixels, read image data are digitally processed, and obtained digital signals are output to a color printer, thereby obtaining a digital color hard copy. Since an apparatus of this type can digitally process image data, various image processes are available, and an application range in the field of color copy tends to be widened. In the image process modes, an output position of an image is shifted (FIG. 72A), a desired image area is extracted (FIG. 72B), only a color in a desired area is converted (FIG. 72C), a character or image stored in a memory is fitted in a reflective original (FIG. 72D), and so on.
Therefore, upon combination of various functions, a digital color copying machine can be easily applied to color planning reports, advertising posters, sales promotion references, design drawings, and the like.
Requirements for outputting images and characters to be worthy of their names are increasingly arisen for a color reflective original. In order to meet these requirements, character and image portions are separated by image area separation, so that high-resolution processing is performed for the character portion, in particular, processing for printing black characters in only black color is performed, and multigradation processing is performed for the image portion. This technique is disclosed in an application by the same assignee as the present invention (U.S. Pat. No. 4,958,219 and U.S. patent application Ser. No. 327,098).
As a conventional method of identifying characteristics of an image, many image area separation methods for judging dots or continuous gradation areas utilizing spatial frequency characteristics or autocorrelation characteristics of images have been proposed.
However, most of the prior art employs a Fourier transformation or an autocorrelation function to utilize frequency characteristics of images, resulting in complex calculations and a limited processing speed. Since an input dot image is not always an ideal dot image or a smoothly and continuously changing image due to an S/N ratio or blurring of an image input system, an error judgement frequently occurs. When a continuous gradation area is judged, input pixels are binarized, and continuity in a binary halftone image is judged, thereby judging a continuous gradation image. Upon binarization, a continuous gradation portion is preferably smooth data. However, actual image data is influenced by S/N ratios of an image input system and a processing system, and binary signals including many deflection points of "1" to "0" and "0" to "1" are obtained. As a result, the binary signals are not easily judged as a continuous tone area.
When Laplacian processing is performed and outline extraction and character area judgement are performed based on the processing result, the following drawbacks are posed, and an error judgement frequently occurs:
(1) Obtained binary signals are weak against noise. PA1 (2) A circuit scale is increased.